Fatty acids and triacylglycerides have a various applications in the food industry, in animal feed, supplement nutrition, and in the cosmetic and pharmacological field. The individual applications may either require free fatty acids or triacylglycerides. In both cases, however, polyunsaturated fatty acids either free or esterified are of pivotal interest for many of the aforementioned applications. In particular, polyunsaturated omega-3-fatty acids and omega-6-fatty acids are important constituents in animal and human food. These fatty acids are supposed to have beneficial effects on the overall health and, in particular, on the central nervous system, the cardivovascular system, the immune system, and the general metabolism. Within traditional food, the polyunsaturated omega-3-fatty acids are mainly found in fish and plant oils. However, in comparison with the needs of the industry and the need for a beneficial diet, this source is rather limited.
The various polyunsaturated fatty acids (PUFA) and PUFA-containing triglycerides are also mainly obtained from microorganisms such as Mortierella and Schizochytrium or from oil-producing plants such as soybean or oilseed rape, algae such as Crypthecodinium or Phaeodactylum and others, where they are usually obtained in the form of their triacylglycerides. The free PUFA are usually prepared from the triacylglycerides by hydrolysis. However, long chain polyunsaturated fatty acids (LCPUFA) having a C-18, C-20, C-22 or C-24 fatty acid body, such as docosahexaenoic acid (DHA), eicospentaenoic acid (EPA), arachidonic acid (ARA), dihomo-gamma-linolenic acid or docosahexaenoic acid (DPA) cannot be efficiently isolated from natural oil crop plants such as oilseed rape, soybean, sunflower or safflower. Conventional natural sources of these fatty acids are, thus, merely fish, such as herring, salmon, sardine, redfish, eel, carp, trout, halibut, mackerel, zander or tuna, or algae.
Especially suitable microorganisms for the production of PUFA in industrial scale are microalgae such as Phaeodactylum tricornutum, Porphoridium species, Thraustochytrium species, Schizochytrium species or Crypthecodinium species, ciliates such as Stylonychia or Colpidium, fungi such as Mortierella, Entomophthora or Mucor and/or mosses such as Physcomitrella, Ceratodon and Marchantia (Vazhappilly 1998, Botanica Marina 41: 553-558; Totani 1987, Lipids 22: 1060-1062; Akimoto 1998, Appl. Biochemistry and Biotechnology 73: 269-278). Strain selection has resulted in the development of a number of mutant strains of the microorganisms in question which produce a series of desirable compounds including PUFA. However, the mutation and selection of strains with an improved production of a particular molecule such as the polyunsaturated fatty acids is a time-consuming and difficult process. This is why recombinant methods as described above are preferred whenever possible. However, only limited amounts of the desired PUFA or LCPUFA and, in particular, DHA or EPA, can be produced with the aid of the above mentioned microorganisms, and, depending on the microorganism used, these are generally obtained as fatty acid mixtures of, for example, EPA, DPA and DHA.